1. Field of the Invention
The present invention relates to a liquid crystal apparatus exhibiting spontaneous polarization and, more particularly, to a liquid crystal apparatus using a ferroelectric liquid crystal (FLC).
2. Related Background Art
A ferroelectric liquid crystal (FLC) as a liquid crystal exhibiting the spontaneous polarization has received a great deal of attention in favor of advantages such as high-speed response and good memory characteristics and has been actively developed to obtain a light bulb and the like. Targets utilizing the above advantages are an optical shutter array, a high-definition display unit by simple matrix driving, a light bulb for high-density recording combined with a photoconductive body. In addition, the ferroelectric liquid crystal is expected to display a motion picture by active matrix driving using thin film transistors (TFTs). These characteristics are disclosed in U.S. Pat. No. 4,840,462, the Proceeding of the SID, Vol. 30/2, 1989 "Ferroelectric Liquid Crystal Video Display", and the like.
In driving of the FLC, the following problems are posed generally or found to be caused as a result of experiments conducted by the present inventors.
One of the problems is a decrease in response speed of the liquid crystal when a direct current (DC) component is continuously applied to the FLC for a long period of time due to the following reason. Localization of internal ions in the liquid crystal is assumed to be induced to form an electric field.
To solve this problem, the present applicant made a proposal (Japanese Patent Application No. 2-69547) for canceling a DC component by an auxiliary pulse. In addition, since an FLC has spontaneous polarization, an electric field is formed by internal ions localized in correspondence with this spontaneous polarization, and a desired gradation image becomes unstable. It is found that hysteresis occurs in optical response to an external voltage value (applied voltage value).
The phenomenon occurring upon application of a reset pulse and a write pulse continuously to the FLC at a drive frequency of about a television rate (60 Hz) will be described with reference to FIGS. 20 to 22.
In consideration of the problems found in the above experiments, in order to stably obtain a gradation image (gradation display) at a television rate in the FLC optical response, the present inventors have made further extensive studies in detail.